Converting solar energy to electric power holds great promise as a renewable clean energy source. Efforts have been made to improve solar-to-electric conversion efficiency of solar cells and to develop devices that redirect relatively more sunlight onto solar cell surfaces. Other efforts have been made to develop solar tracking systems that can reposition solar cells to follow the sun, but these systems typically require costly and complex tracking devices and actuator systems that consume power for repositioning the solar cells which reduces the net gain of the system because of the power consumed to reposition the solar cells. Such systems have not proven to be cost efficient. Yet other efforts have been made to try to provide artificial heliotropism-type movements for repositioning the solar cells with actuators made from light-induced shape-memory materials, but such materials have proven to provide less actuation than is desirable and tend to fatigue and fail quickly.
Therefore, it is a primary object and feature of the present invention to provide a passive solar tracking system to enhance solar cell output.
It is a still further object and feature of the present invention to provide a solar tracking system having a panel with solar cells that passively tracks and continuously faces the sun.
It is a further object and feature of the present invention to provide a passive solar tracking system to enhance solar cell output by providing actuators that are directly driven by sunlight to provide artificial heliotropism-type movements of the panel.
It is a further object and feature of the present invention to provide a passive solar tracking system to enhance solar cell output by providing actuators that are directly driven by sunlight and actuator housings that are arranged to enhance delivery of sunlight-based stimulus to the actuators.
In accordance with the present invention, a passive solar tracking system to enhance solar cell output is provided that includes a panel having at least one solar cell for solar-to-electric conversion. The panel may be supported on a flexible support extending between the panel and an underlying support surface, such as the ground. The panel is movable for providing a variable facing direction. An actuator is arranged for moving the panel to provide the variable facing direction of the panel. Multiple actuators may be provided for moving the panel based on desired movement characteristics. The actuator(s) may have a variable length that varies in response to a stimulus for driving movement of the panel. The stimulus may have multiple stimuli components, which may include a photo stimulus such as a light-based stimulus as a first stimulus component and a thermal-based stimulus such as heat-based stimulus as a second stimulus component. This may allow the actuator(s) to be directly driven by sunlight to provide artificial heliotropism-type movements of the panel so that the panel passively tracks and continuously faces the sun without parasitically drawing power from the system or otherwise requiring ancillary power for moving the panel.
In accordance with another aspect of the invention, the actuator(s) may be made from a composite material fabricated by way of, for example, a multi-stage cross-linking procedure coupled with a drawing procedure. The composite material may include a matrix of a liquid crystal elastomer material having properties of both liquid crystals and elastomers, which may define photo-thermo-mechanical properties, so as to define reversible dimensional changes which may be anisotropic dimensional changes in response to applied stimulus. Carbon nanostructures, which may be carbon nanotubes such as single-wall or multi-wall carbon nanotubes, may be dispersed through the matrix of a liquid crystal elastomer material. The carbon nanotubes can efficiently absorb and convert photon energy into thermal energy and have excellent thermal conductivities. This allows the carbon nanotubes to act as nanoscale heat sources and provide a thermal conduction pathway to effectively heat the liquid crystal elastomer matrix, elevating its temperature to above its nematic-isotropic transition temperature, changing the nematic order, and leading to a reversible axial contraction and mechanical actuation. An elastic skeleton is arranged within the composite material and includes a fiber network which may be a 3D polyurethane-based fiber network may also be dispersed through the matrix of liquid crystal elastomer material, providing a reinforcement phase into the matrix of liquid crystal elastomer material. This may provide a nematic-phase texture of the composite material that has mesogenic units that are substantially uniaxially aligned. Correspondingly, the nematic-isotropic transition temperature of the composite material may be significantly lower when incorporating the polyurethane fiber network along with carbon nanostructuers, as compared to without the polyurethane fiber network and may be less than about 70° C. or less than about 68° C. This may provide an actuator(s) that has a nematic-isotropic transition temperature that is sufficiently low to allow for actuation that is directly driven by sunlight.
In accordance with another aspect of the invention, the passive solar tracking system may include an actuator housing for each of the actuators that surrounds at least a portion of the respective actuator for facilitating delivery of the stimulus to the actuator. The actuator housing may include a heat collector arranged to direct heat toward the actuator. The heat collector may be defined at least partially by a body of the actuator housing through which a cavity may longitudinally extend such that at least a portion of the actuator is arranged in the cavity of the body. The cavity may define a partial cylindrical shape corresponding to a section of a cylinder that extends longitudinally through the cylinder. The body of the actuator housing may have a dark color and may be made from a black polymeric material such as a polytetrafluoroethylene material. This may enhance heat capacitance of the actuator housing which may correspondingly enhance actuation of the actuator.
In accordance with another aspect of the invention, the actuator housing may include a light concentrator arranged to direct sunlight toward the actuator. The light concentrator may define a curved surface for directing the sunlight toward the actuator, which may define a reflective wall extending generally parallel to and transversely spaced from the actuator. The curved surface may be configured to focus the sunlight onto the actuator. The reflective wall may be made from a silver and/or mercury coated glass or may include a reflective film, such as a multilayer polymer film. The light concentrator may include a clear wall that may be made from a clear material such as a high-transmittance material that attenuates light by a relatively nominal extent. The clear wall allows ambient light to transmit through it and directly onto the actuator, for example, onto an outer surface of the actuator. The clear and reflective walls may be spaced from each other and define the outer perimeter of the cavity through which the actuator extends. Ambient light transmitted through the clear wall but around the actuator may be reflected off the reflective wall and directed to the actuator, for example, onto an inner surface of the actuator. This may allow the actuator to simultaneously receive sunlight on both a side that faces the sun and a side that faces away from the sun which may enhance actuation of the actuator.